The present invention relates generally to magnetic flowmeters and, more particularly, to a magnetic flowmeter having a sensor assembly that forms a moisture barrier while providing accurate flow measurements.
Magnetic flowmeters are used to measure the flow of electrically conductive fluids such as water through a conduit or pipeline. Such flowmeters measure the flow or velocity of the fluid moving through the pipeline by using Faraday's Law. Faraday's Law states that a conductor moving through a magnetic field produces a voltage. For example, water is a conductor so it produces a voltage when it passes through a magnetic field. The magnitude of the voltage is directly proportional to the velocity at which the fluid, i.e., water, moves through the magnetic field.
Conventional flowmeters include electromagnetic coils inside a sensor that produce magnetic fields, and electrodes on the sensor that measure the voltage generated by a fluid moving through those magnetic fields. The planes of the magnetic fields are typically oriented transverse so that a conductive fluid passes through the magnetic fields, a voltage is induced. The flowmeters typically include a plurality of electrodes that are spaced apart from each other and in electrical contact with the fluid to measure the induced voltage. The measured voltage is used to determine the average velocity of the fluid flowing through the conduit.
Most flowmeters include a sensor or sensor assembly including a magnetic source and one or more sets of electrodes. The sensor assembly is positioned so that the electrodes are in contact with the fluid flowing through the conduit. To obtain an accurate velocity measurement, it is beneficial to maintain a magnetic field within the measured region between the electrodes. It's also important to prevent moisture from contacting and damaging the interior circuitry, which leads to inaccurate measurements.
Existing flowmeters typically include a body enclosing or extending into the fluid column. The flowmeters incorporate sensing electrodes, one end of which extends into the fluid and an opposing end extends at least partially into the body where wiring connected to the electrodes passes through an interior space in the body that includes the magnetic coils. The openings in the body create a pathway for moisture to enter the interior and expose the inner circuitry to moisture from the fluid in the conduit. The likelihood that moisture will move through the pathway and enter the interior of the sensor increases as the fluid pressure inside the pipeline increases. Such moisture affects the operation of the inner circuitry and leads to inaccurate flow measurements due to malfunction or failure and increases repair and replacement costs. Existing sensors are therefore limited to pipelines having pressures at or below 1000 psi (pounds per square inch). Above 1000 psi, existing sensors are not able to prevent moisture from entering the interior of the sensor. In addition to pressure limitations, some existing sensors have a porous plastic body which also allows moisture to be absorbed by and enter the body over time.
Thus, there is a need for a flowmeter that provides an impermeable barrier against moisture while also providing accurate flow measurements.